GUATEMALA CITY (AP) _ Negotiators for Nicaraguan rebels say the U.S. refusal of more aid has not changed their position for the second round of peace talks Thursday with the Sandinista government.

Fernando Aguero, one of the seven Contra delegates, told reporters after arriving Wednesday that the rebels still want three-way talks including the internal Nicaraguan opposition and they still want to discuss political matters.

The leftist Nicaraguan government insists on sticking to the mechanics of arranging a 30-day cease-fire that could lead to a permanent truce. It says political changes will be discussed only after the Contras have accepted an amnesty, laid down their arms and resumed civilian life within the country.

Aguero, the rebel delegate, said: ''Our position has not changed, and it will not change. There can be no cease-fire unless the Sandinistas first agree to democratic reforms in Nicaragua.''

The first direct talks were held in San Jose, Costa Rica, last month, a week before the House of Representatives voted down President Reagan's request for another $36.2 million in Contra aid.

The rebels and the Nicaraguan government each presented radically different proposals in a two-day session that all said was noted for cordiality and lack of progress. Several diplomatic observers suggested neither side wanted to rock the boat before the congressional vote.

Cardinal Miguel Obando y Bravo, Roman Catholic primate of Nicaragua, will mediate the Guatemala City talks. He was visiting Rome on Vatican business during the San Jose session and sent a substitute.

Obando y Bravo is scheduled to arrive at mid-morning and the talks probably will begin in the afternoon at the Guatemala archbishopric. They are scheduled to end Saturday.

Victor Hugo Tinoco, deputy foreign minister, will lead the Nicaraguan delegation. Jaime Morales Carazo, a former Managua banker, heads the Contra group.

The talks are being held in line with a Central American peace plan signed last August by by Nicaragua, El Salvador, Honduras, Costa Rica and Guatemala.